It is known that air turbulence corresponds to an agitation that is superimposed on the mean movement of the air and that is made up of continually changing disordered movements. The turbulence is encountered in or in the vicinity of the clouds (for example, in a stormy cloud where vertical currents in opposite directions coexist). There is also turbulence in clear sky, either close to the ground, or, primarily, at very high altitude in the vicinity of the jet streams.
It is also known that turbulence has, in recent years, been the primary cause of injuries in civil aviation. This is linked mainly to a negative load factor of the airplanes.
The airplanes are equipped with meteorological radars with which to create a map of precipitations, and this normally up to a distance of 100 nautical miles (approximately 185 kilometers) in front of the airplane, and detect particular risks such as the turbulences within a radius of 40 nautical miles (approximately 74 kilometers) and “windshear” type phenomena within a radius of 10 nautical miles (approximately 18 kilometers).
However, the meteorological radars can only detect turbulences, for which the drops of water have an adequate diameter. This is why the turbulences in clear sky (dry air masses) cannot be detected.
Furthermore, even the cloud masses cannot be totally detected. For example, a cumulonimbus which contains extremely dynamic and very rapid significant turbulent phenomena comprises, in its top part, ice crystals. The latter reflect little and are therefore almost  invisible to a meteorological radar. Also, the turbulences associated with the top part of a cumulonimbus are almost undetectable.